refactor(core): remove dead AISDK hook domain

[kitlangton]

What

Remove the unused aisdk member from Core's generic PluginHooks.Domains type map.

The active AISDK plugin API is a separate path: PluginHost maps ctx.aisdk hooks directly to AISDK.Service. This change removes only generic registry typing that has no registrations or triggers.

Before / After

Before: PluginHooks.Domains advertised an aisdk domain even though no repository caller registered or triggered an AISDK hook through the generic PluginHooks service.

After: PluginHooks.Domains describes only its used session, shell, and tool domains. Live Promise and Effect AISDK plugin hooks continue through PluginHost and AISDK.Service unchanged.

How

• Remove the type-only AISDKHooks import from packages/core/src/plugin/hooks.ts.
• Remove the readonly aisdk: AISDKHooks member from PluginHooks.Domains.
• Confirm repository-wide that no generic register("aisdk", ...) or trigger("aisdk", ...) consumers exist.

Flow

flowchart LR
  subgraph removed["Removed: dead generic typing"]
    domain["PluginHooks.Domains.aisdk<br/>(type only)"] -. "no register/trigger callers" .-> registry["Generic PluginHooks registry"]
  end

  subgraph live["Unchanged: live AISDK hooks"]
    host["PluginHost<br/>ctx.aisdk adapter"] --> service["AISDK.Service"] --> provider["Provider hook callback"]
  end

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Scope

This deliberately does not change AISDK.Service, plugin host adapters, Promise or Effect plugin contracts, provider registrations, AISDK documentation, or tests for active AISDK behavior.

Testing

• bun run test test/plugin-hooks.test.ts from packages/core (2 passed)
• bun typecheck from packages/core
• bunx oxlint packages/core/src/plugin/hooks.ts
• bunx prettier --check packages/core/src/plugin/hooks.ts
• Push hook: bun turbo typecheck --concurrency=3 (33 tasks successful)
• Repository-wide search confirmed no generic register("aisdk") or trigger("aisdk") consumers